hs-hide-all gives unbalanced parentheses error when it shouldn't in some Rnw buffers

[rdiaz02]

Running hs-hide-all (from hs-minor-mode) can lead to Scan error: "Unbalanced parentheses" when it shouldn't; once that happens, other things fail, like syntax highlighting.
It seems that hs-hide-all continues scanning beyond the boundaries of the code chunk.

This is an exampe.

1. Do emacs -Q and evaluate

(package-initialize)
(add-hook 'prog-mode-hook (lambda () (hs-minor-mode 1) (hs-hide-all)))

2. Suppose this Rnw file:

\documentclass{article}

\usepackage{color}
\newcommand{\blu}[1]{\textcolor{blue}{#1}}

\begin{document}

<<>>=
f1 <- function(x) {
  return(2 * x)
}
@ 

\end{document}

If we find-file the file, we get

Polymode error (pm--mode-setup ’ess-r-mode): Scan error: "Unbalanced parentheses", 65, 169

That error disappears if:

1. The Rnw file does not have the line \newcommand{\blu}[1]{\textcolor{blue}{#1}} or that line is commented out. The culprit seems to be the # .
2. You load the file, but the hook does not include the hs-hide-all. In this second case, the file loads without error, but you can trigger the error by M-x hs-hide-all in the R chunk.

For now, a workaround I am using is to modify the hook, so that if the file ends on Rnw (and, since I am at it, in Rmd) hs-minor-mode is not enabled (or hs-hide-all is not called). (For anybody encountering this problem, this is what I do, and seems to work but, caveat emptor, this is from a complete elisp newby:

(defun prog-mode-hook-no-hide-all-in-polym ()
  "hs-minor-mode and hs-hide-all, but in Rnw and Rmd
do not hs-hide-all, because it can break polymode.
I am not sure this only disables hs-hide-all : I think hs-minor-mode is 
not enabled in ESS chunks. Well, no big deal for now."
  (hs-minor-mode 1)
  (unless (and (buffer-file-name)
               (or (string-match-p "\\.Rnw\\'" (buffer-file-name))
                   (string-match-p "\\.Rmd\\'" (buffer-file-name))))
    (hs-hide-all)))


(add-hook 'prog-mode-hook 'prog-mode-hook-no-hide-all-in-polym)